1. Field of the Invention
The present invention relates to a compound bearing assembly and a method of manufacturing the same, the compound bearing assembly being used in rotating portions of a computer and its peripheral devices.
2. Description of the Prior Art
As for a conventional compound bearing assembly constructed of a pair of ball bearing units A, B mounted on a rotary shaft D of rotating portions of a computer or its peripheral devices, as is clear from FIG. 4(a), it is necessary to produce its components separately. Consequently, a sleeve-like spacer C and such pair of the ball bearing units A, B are produced separately from each other. These components A, B, C of the conventional compound bearing assembly are then delivered to a user. After receipt of the components, the user mounts the components A, B, C on the rotary shaft D to complete the conventional compound bearing assembly, as shown in FIG. 4(b).
As described above, in the conventional compound bearing assembly, it is necessary for the user to mount the pair of the ball bearing units A, B and the spacer C on the rotary shaft D in a condition in which the ball bearing units A, B are spaced apart from each other through the spacer C. Consequently, the conventional compound bearing assembly suffers from the following problems:
(a) While keeping a sufficient rigidity, the rotary shaft D is required to be sized in outer diameter so as to engage with the inner race rings of the ball bearing units A, B; PA1 (b) Since the spacer C is a separate component independent of the pair of the ball bearing units A and B, it is necessary for the spacer C to have its opposite end surfaces improved in parallelism therebetween and also in flatness thereof, taken in connection with the dimensions of the ball bearing units A, B being assembled together with the spacer C; and PA1 (c) Since the spacer C is merely sandwiched between a pair of outer race rings of the ball bearing units A and B, it is necessary for the user to have the spacer C coaxially mounted on the rotary shaft D with high accuracy, which requires the spacer C to have its opposite axial end surfaces brought into uniform contact with axially inner end surfaces of the outer race rings of the ball bearing units A, B, and, therefore takes much time and labor. PA1 (a) a stepped-diameter shaft is provided with a large-diameter portion, a small-diameter portion and an inner raceway groove directly formed in an outer peripheral surface of the large-diameter portion of the shaft; PA1 (b) the stepped-diameter shaft is encircled by a sleeve-like outer race ring which is provided with a single-piece outer race ring in one of its axially opposite ends and an outer raceway groove in an inner peripheral surface of the other of the axially opposite ends; and PA1 (c) a plurality of first balls rotatably mounted in the inner raceway groove of the large-diameter portion of the shaft are held by the outer raceway groove of the single-piece outer race ring, and a plurality of second balls rotatably mounted in the inner raceway groove of the inner race ring are held by the outer raceway groove of the sleeve-like outer race ring or by that of the single-piece outer race ring. PA1 the compound bearing assembly as set forth in the first aspect of the present invention, wherein: PA1 the first balls around the inner raceway groove of the large-diameter portion are held by the outer raceway groove of the single-piece outer race ring; and PA1 the second balls around the inner raceway groove of the inner race ring mounted on the small-diameter portion are held by the outer raceway groove of the sleeve-like outer race ring. PA1 the compound bearing assembly as set forth in the first aspect of the present invention, wherein: PA1 the first balls around the inner raceway groove of the large-diameter portion of the shaft are held by the outer raceway groove of the sleeve-like outer race ring; and PA1 the second balls around the inner raceway groove of the inner race ring mounted on the small-diameter portion are held by the outer raceway groove formed in an inner peripheral surface of the outer race ring. PA1 a stepped-diameter shaft is provided with a large-diameter portion, a small-diameter portion and an inner raceway groove directly formed in an outer peripheral surface of the large-diameter portion of the stepped-diameter shaft; PA1 the stepped-diameter shaft is encircled by a sleeve-like outer race ring which is provided with a single-piece outer race ring in one of its axially opposite ends and an outer raceway groove in an inner peripheral surface of the other of the axially opposite ends; PA1 a plurality of first balls rotatably mounted in the inner raceway groove of the large-diameter portion of the shaft are held by the outer raceway groove of the single-piece outer race ring, and a plurality of second balls rotatably mounted in the inner raceway groove of the inner race ring are held by the outer raceway groove of the sleeve-like outer race ring or by that of the outer race ring; PA1 in a condition in which a predetermined pre-load is applied to an outer end portion of the inner race ring or of the sleeve-like outer race ring, the inner race ring is firmly bonded to the small-diameter portion of the stepped-diameter shaft by means of an adhesive; PA1 whereby the components such as the sleeve-like outer race ring, single-piece outer race ring, inner race ring and the like are assembled together with the stepped-diameter shaft into a compound bearing assembly. PA1 the method of manufacturing the compound bearing assembly, as set forth in the fourth aspect of the present invention, wherein: PA1 the first balls around the inner raceway groove of the large-diameter portion of the shaft are held by the outer raceway groove of the single-piece outer race ring; and PA1 the second balls around the inner raceway groove of the single-piece outer race ring are held by an outer raceway groove of the sleeve-like outer race ring, the outer raceway groove being formed in an inner peripheral surface of the sleeve-like outer race ring. PA1 the method of manufacturing the compound bearing assembly, as set forth in the fourth aspect of the present invention, wherein: PA1 the first balls around the inner raceway groove of the large-diameter portion of the shaft are held by the outer raceway groove of the sleeve-like outer race ring; and PA1 the second balls around the inner raceway groove of the inner race ring mounted on the small-diameter portion of the shaft are held by an outer raceway groove of the outer race ring, the outer raceway groove being formed in an inner peripheral surface of the outer race ring. PA1 a compound bearing assembly characterized in that: PA1 an inner raceway groove is directly formed in an outer peripheral surface of a large-diameter portion of a stepped-diameter shaft which is provided with a small-diameter portion together with the large-diameter portion; PA1 first balls disposed between the inner raceway groove and an outer raceway groove which is formed in an inner peripheral surface of a single-piece outer ring mounted around the large-diameter portion; PA1 a ball bearing unit has its inner race ring mounted on the small-diameter portion of the stepped-diameter shaft and its balls disposed between its inner and its outer race ring; and PA1 a sleeve-like spacer is axially sandwiched between the outer race ring of the ball bearing unit and the single-piece outer ring. PA1 a method of manufacturing a compound bearing assembly is characterized in that: PA1 an inner raceway groove is directly formed in an outer peripheral surface of a large-diameter portion of a stepped-diameter shaft which is provided with a small-diameter portion together with the large-diameter portion; PA1 first balls disposed between the inner raceway groove and an outer raceway groove which is formed in an inner peripheral surface of a single-piece outer ring mounted around the large-diameter portion; PA1 a ball bearing unit has its inner race ring slidably mounted on the small-diameter portion of the stepped-diameter shaft and its balls disposed between its inner and its outer race ring; PA1 a sleeve-like spacer is axially sandwiched between the outer race ring of the ball bearing unit and the single-piece outer ring; and PA1 the inner race ring of the ball bearing unit is fixed to the small-diameter portion of the stepped-diameter shaft in a condition in which a predetermined pre-load is applied to an outer end surface of one of the inner and the outer race ring of the ball bearing unit.